Java HashMap<String,List<String>>() Comparison

Question

I'm wondering the best way to compare these two HashMaps. I want to verify if they are the same, and if not, what is the difference. If it matters, then I'm wondering what the 2nd one has/does not have that the first hashmap does have. I'll need to know if one has a key the other does not, as well as the Value List differences per key. I'm hoping there is a simple way to map this, but not sure. Basic Example:

    HashMap<String, List<String>> hmOne = new HashMap<String, List<String>>();
    List<String>l1 = new ArrayList<String>();

    l1.add("one");
    l1.add("two");
    l1.add("three");
    l1.add("four");
    l1.add("five");
    hmOne.put("firstkey", l1);
    l1 = new ArrayList<String>();

    l1.add("1");
    l1.add("2");
    l1.add("3");
    l1.add("4");
    l1.add("5");
    hmOne.put("secondkey", l1);

    HashMap<String, List<String>> hmTwo = new HashMap<String, List<String>>();
    List<String>l2 = new ArrayList<String>();
    l2.add("one");
    l2.add("two");
    l2.add("four");
    l2.add("five");
    hmTwo.put("firstkey", l2);
    l2 = new ArrayList<String>();

    l2.add("1");
    l2.add("3");
    l2.add("4");
    l2.add("5");
    hmTwo.put("secondkey", l2);

Thanks for any help.

Answer 1

guava有Maps.difference(map1, map2)

Answer 2

HashMap.equals will tell you if they are identical (same keys and values) but the rest you will have to roll yourself.

You will need to iterate the keyset() of one HashMap , look for it in the keySet() of the other and if found then compare the values.

Then, you will have to do the reverse, looking for keys in the second that don't exist in the first. You can probably use Set methods for this.

Answer 3

You know that Map's .equals() method will tell you if two Maps are equal, right?

If they aren't equal, you're going to have to parse them both and figure out the differences on your own.

Answer 4

Off the top of my head, you could first use HashMap.equals() to tell if they are different and then get the keySet of each hashmap and compare them:

What is the fastest way to compare two sets in Java?

Then once you've got the differences in keys, you could repeat the process on your value collections.